Generally, a fabricated article made from a polymeric material can become statically charged, and the surface can attract and hold charged particles such as dust in the air. In some cases an article can become damaged and/or otherwise devalued by the adhesion of electrostatically charged species.
Accordingly, antistatic properties may be important for many applications for preventing adhesion of charged particles. Except for polymers of inherently high polarity, most organic polymeric materials lack adequate antistatic resistance especially at low humidity. This is especially true for polyolefin materials, such as polypropylene, polyethylene, and ethylene copolymers, etc.
Many attempts have been made to address this issue from aspects of performance, cost, and ease of conversion to final products. Antistatic agents can be incorporated into the composition of a molded article or an antistatic agent can be applied to the surface of an article as a way of preventing build-up of static charge on an article. Use of antistatic agents is not trouble-free.
A common approach to enhancing the antistatic properties of thermoplastics is to introduce low-molecular weight antistatic agents into the polymeric material by compounding prior to or during the manufacturing of articles, e.g., by means of molding or film-forming processes. Antistatic agents work by migrating to the external polymer surface of the manufactured articles because of their high volatility and poor compatibility with polymer composition. They form a continuous film on the surface of the polymers. Therefore, the incorporation of a low-molecular weight antistatic agent for achieving anti-static is not trouble free. Materials that come in contact with the composition can become contaminated due to bleeding of the antistatic agent out of the composition and/or the antistatic agent effect can be deteriorated with time.
An applied antistatic film can have inadequate mechanical properties and could be easily damaged, or have poor water resistance, or become tacky due to absorption of water.
Another commonly practiced approach is to add permanent, non-diffusing antistatic agents based on polymers with high antistatic properties. For example, block copolymers based on polyether-block-amide (commercially supplied by Atochem under the PEBAX® tradename) may be used as permanent antistatic agents by compounding with an isolative polymer to lower the surface resistivity.
While polyether-block-amides may perform well in certain polymer systems, they do not perform well with polyolefin systems. Due to their poor compatibility with polyolefin materials, a third polymer serving as a compatibilizer may have to be added to insure the antistatic function of the polyolefin matrix. This may confine the composition to be processed in a narrow processing window for attaining the antistatic performance. Polyetheramide block copolymers do not have suitable direct adhesion to other substrates, especially polyolefin substrates. Their high cost is another issue for their use as permanent antistatic agents.
U.S. Pat. No. 5,001,015 discloses polyolefin films with antistatic properties which include as possible antistatic agents the reaction products of polyalkoxylates with fatty alcohols.
Potassium-neutralized ionomer compositions have been developed to act as permanent antistatic agents in blending with polyolefins (see e.g. PCT Patent Application publication WO2004-050362). K-ionomer compositions may function well as permanent antistatic agents, but they are difficult to produce and handle in initial manufacture and when converting into final products. See also US Patent Application Publication 2007/0142542.
Subsurface antistatic polymer layers can be used to avoid problems encountered with exposing an antistatic layer at the surface of an article. JP 2-28919B discloses an antistatic plastic film in which an ionic conductive resin layer is formed on a plastic film and a waterproof plastic layer having a volume resistivity of 1×1013 Ω·cm or less and having a thickness of 10 μm or less is formed on the surface of the ionic conductive resin layer.
JP 61-44646A discloses a charged stain-resistant laminate having an alkali metal salt or amine salt of an ethylene-unsaturated carboxylic acid copolymer as an intermediate layer. JP 10-193495A discloses a dustproof laminate having a composition comprising a thermoplastic resin consisting of a potassium ionomer of an ethylene-unsaturated carboxylic acid and a polyhydroxy compound as an intermediate layer.
Overall, a satisfactory solution for polyolefin-based materials with adequate anti-static performance has not been achieved.